Telecommunications apparatus and methods

ABSTRACT

Schemes for supporting device-to-device, D2D, communications between terminal devices in a wireless telecommunication system. A network entity, e.g. a base station, establishes a set pool of radio resources to be reserved for use for D2D communications and communicates an indication of these resources to terminal devices. On an ongoing basis the network entity monitors the extent to which the set of radio resources reserved for D2D communications is being used, for example based on feedback received from terminal devices or its own measurements. If it is determined the set of radio resources reserved for D2D communications is being under-utilized or over-utilized, the network entity may establish an updated set of radio resources to be used for D2D communications, and communicate this to the terminal devices. Thus a mechanism is provided for dynamically adjusting the size of a set of resources available for D2D communications in response to changing resource utilization.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/126,153, filed Sep. 14, 2016, which is based on PCT filingPCT/EP2015/055163, filed Mar. 12, 2015, which claims priority to EP14161181.4, filed Mar. 21, 2014, the entire contents of each areincorporated herein by reference.

BACKGROUND Field

The present disclosure relates to telecommunications apparatus andmethods, and in particular to telecommunications apparatus and methodsfor use in wireless telecommunications systems in which terminal devicesare configured to perform device-to-device communications.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Mobile telecommunication systems, such as those based on the 3GPPdefined UMTS and Long Term Evolution (LTE) architecture, are able tosupport more sophisticated services than simple voice and messagingservices offered by previous generations of mobile telecommunicationsystems. For example, with the improved radio interface and enhanceddata rates provided by LTE systems, a user is able to enjoy high datarate applications such as video streaming and video conferencing onmobile communications devices that would previously only have beenavailable via a fixed line data connection.

The demand to deploy fourth generation networks is therefore strong andthe coverage area of these networks, i.e. geographic locations whereaccess to the networks is possible, is expected to increase rapidly.However, although the coverage and capacity of fourth generationnetworks is expected to significantly exceed those of previousgenerations of communications networks, there are still limitations onnetwork capacity and the geographical areas that can be served by suchnetworks. These limitations may, for example, be particularly relevantin situations in which networks are experiencing high load and high-datarate communications between communications devices, or whencommunications between communications devices are required but thecommunications devices may not be within reliable coverage of a network.In order to address these limitations there have been proposedapproaches in which terminal devices (communications devices) within awireless telecommunications system may be configured to communicate datadirectly with one another without some or all communications passingthrough an infrastructure equipment element, such as a base station.Such communications are commonly referred to as a device-to-device (D2D)communications. It is expected that D2D communications will beintroduced in LTE release-12.

Thus, D2D communications allow communications devices that are insufficiently close proximity to directly communicate with each other,both when within the coverage area of a network and when outside anetwork's coverage area (e.g. due to geographic restrictions on anetwork's extent or because the network has failed or is in effectunavailable to a terminal device because the network is overloaded). D2Dcommunications can allow user data to be more efficiently communicatedbetween communications devices by obviating the need for user data to berelayed by a network entity such as a base station, and also allowscommunications devices that are in sufficiently close proximity tocommunicate with one another when one or both devices may not be withinthe reliable coverage area of a network. The ability for communicationsdevices to operate both inside and outside of coverage areas makes LTEsystems that incorporate D2D capabilities well suited to applicationssuch as public safety communications, for example. Public safetycommunications may benefit from a high degree of robustness wherebydevices can continue to communicate with one another in congestednetworks and when outside a coverage area.

Fourth generation networks have therefore been proposed as a costeffective solution to public safety communications compared to dedicatedsystems such as TETRA (terrestrial trunked radio) which are currentlyused throughout the world.

The inventors have recognised one issue for consideration for D2Dcommunications is how much radio resource should be reserved forsupporting D2D communications in a wireless telecommunications network.A wireless telecommunications network generally supports communicationsover a wireless access interface comprising an array (grid) of time andfrequency resources. In order to support D2D communications, at least insome modes of D2D operation, it is expected that a portion of anetwork's available resources will be reserved for D2D use. Radioresources which are reserved for supporting D2D communications in thisway may sometimes be referred to herein as a D2D resource pool. Theinventors have recognised in particular that the size of a D2D pool in agiven implementation can be an important consideration for optimisingnetwork operation.

On the one hand, a relatively large D2D pool can support acorrespondingly large amount of D2D communications, but with acorresponding large reduction in resources available for othercommunications in the network. This means if the resources comprisingthe D2D pool are not being used for D2D communications, the D2D poolwill to some extent represent a waste of at least some resources in thenetwork. On the other hand, a relatively small D2D pool will have acorrespondingly smaller impact on the resources available for othercommunications, but gives rise to increased likelihood of congestion inrespect of D2D communications. That is to say, there can be expected tobe an increased chance of a device being unable to access resources tomake D2D communications because the resources reserved for D2Dcommunications (i.e. the D2D resource pool) are already allocated foruse by other D2D devices. Public safety related activities are expectedto represent one significant application of D2D communications, and forthese applications it can be particularly important to avoid congestion.

The inventors have thus recognised a need for apparatus and methods forhelping to make more efficient use of radio resources in networkssupporting D2D communications while also helping to reduce the extent ofD2D congestion in such systems.

SUMMARY

According to one aspect of the present disclosure, there is provided amethod of operating a network entity in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, the method comprising: establishing a set of radio resources tobe made available for D2D communications within the wirelesstelecommunication system; communicating an indication of the set ofradio resources to terminal devices operating in the wirelesstelecommunications system; determining an indication of an extent towhich the set of radio resources is being used for D2D communications;establishing an updated set of radio resources to be made available forD2D communications within the wireless telecommunication system based onthe indication of the extent to which the set of radio resources isbeing used for D2D communications; and communicating an indication ofthe updated set of radio resources to terminal devices operating withinthe wireless telecommunications system.

According to another aspect of the present disclosure, there is provideda network entity for use in a wireless telecommunication systemsupporting device-to-device, D2D, communications between terminaldevices, wherein the network entity comprises a controller unit and atransceiver unit configured to operate together to: establish a set ofradio resources to be made available for D2D communications within thewireless telecommunication system; communicate an indication of the setof radio resources to terminal devices operating in the wirelesstelecommunications system; determine an indication of an extent to whichthe set of radio resources is being used for D2D communications;establish an updated set of radio resources to be made available for D2Dcommunications within the wireless telecommunication system based on theindication of the extent to which the set of radio resources is beingused for D2D communications; and communicate an indication of theupdated set of radio resources to terminal devices operating within thewireless telecommunications system.

According to another aspect of the present disclosure, there is providedcircuitry for a network entity for use in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, wherein the circuitry comprises a controller element and atransceiver element configured to operate together to cause the networkentity to: establish a set of radio resources to be made available forD2D communications within the wireless telecommunication system;communicate an indication of the set of radio resources to terminaldevices operating in the wireless telecommunications system; determinean indication of an extent to which the set of radio resources is beingused for D2D communications; establish an updated set of radio resourcesto be made available for D2D communications within the wirelesstelecommunication system based on the indication of the extent to whichthe set of radio resources is being used for D2D communications; andcommunicate an indication of the updated set of radio resources toterminal devices operating within the wireless telecommunicationssystem.

According to another aspect of the present disclosure, there is provideda method of operating a terminal device in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, the method comprising: receiving an indication of a set ofradio resources available for D2D communications within the wirelesstelecommunication system from a network entity; determining anindication of an extent to which the set of radio resources is beingused for D2D communications; and transmitting the indication of theextent to which the set of radio resources is being used for D2Dcommunications to the network entity.

According to another aspect of the present disclosure, there is provideda terminal device for use in a wireless telecommunication systemsupporting device-to-device, D2D, communications between terminaldevices, wherein the terminal device comprises a controller unit and atransceiver unit configured to operate together to: receive anindication of a set of radio resources available for D2D communicationswithin the wireless telecommunication system from a network entity;determine an indication of an extent to which the set of radio resourcesis being used for D2D communications; and transmit the indication of theextent to which the set of radio resources is being used for D2Dcommunications to the network entity.

According to another aspect of the present disclosure, there is providedcircuitry for a terminal device for use in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, wherein the circuitry comprises a controller element and atransceiver element configured to operate together to cause the terminaldevice to: receive an indication of a set of radio resources availablefor D2D communications within the wireless telecommunication system froma network entity; determine an indication of an extent to which the setof radio resources is being used for D2D communications; and transmitthe indication of the extent to which the set of radio resources isbeing used for D2D communications to the network entity.

According to another aspect of the present disclosure, there is provideda method of operating a terminal device in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, the method comprising: receiving an indication of a set ofradio resources available for D2D communications within the wirelesstelecommunication system from a network entity; monitoring the set ofradio resources to determine if another terminal device is seeking tocommunicate with the terminal device in a D2D manner using the set ofradio resources; receiving an indication of an updated set of radioresources available for D2D communications within the wirelesstelecommunication system from the network entity; and monitoring theupdated set of radio resources to determine if another terminal deviceis seeking to communicate with the terminal device in a D2D manner usingthe set of radio resources.

According to another aspect of the present disclosure, there is provideda terminal device for use in a wireless telecommunication systemsupporting device-to-device, D2D, communications between terminaldevices, wherein the terminal device comprises a controller unit and atransceiver unit configured to operate together to: receive anindication of a set of radio resources available for D2D communicationswithin the wireless telecommunication system from a network entity;monitor the set of radio resources to determine if another terminaldevice is seeking to communicate with the terminal device in a D2Dmanner using the set of radio resources; receive an indication of anupdated set of radio resources available for D2D communications withinthe wireless telecommunication system from the network entity; andmonitor the updated set of radio resources to determine if anotherterminal device is seeking to communicate with the terminal device in aD2D manner using the set of radio resources.

According to another aspect of the present disclosure, there is providedcircuitry for a terminal device for use in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, wherein the circuitry comprises a controller element and atransceiver element configured to operate together to cause the terminaldevice to: receive an indication of a set of radio resources availablefor D2D communications within the wireless telecommunication system froma network entity; monitor the set of radio resources to determine ifanother terminal device is seeking to communicate with the terminaldevice in a D2D manner using the set of radio resources; receive anindication of an updated set of radio resources available for D2Dcommunications within the wireless telecommunication system from thenetwork entity; and monitor the updated set of radio resources todetermine if another terminal device is seeking to communicate with theterminal device in a D2D manner using the set of radio resources.

Further respective aspects and features are defined by the appendedclaims.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein likereference numerals designate identical or corresponding parts throughoutthe several views, and wherein:

FIG. 1 provides a schematic diagram illustrating an example of a mobiletelecommunication system;

FIG. 2 provides a schematic diagram illustrating a LTE downlink radioframe;

FIG. 3 provides a schematic diagram illustrating an example of a LTEdownlink radio subframe;

FIG. 4 provides a schematic diagram illustrating an example of a LTEuplink radio subframe;

FIG. 5 schematically represents a wireless telecommunications systemaccording to an embodiment of the disclosure; and

FIGS. 6 to 8 are ladder diagrams schematically representing methods ofoperation in accordance with certain embodiments of the disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a mobile telecommunications network/system 100operating in accordance with LTE principles and which may be adapted toimplement embodiments of the disclosure as described further below.Various elements of FIG. 1 and their respective modes of operation arewell-known and defined in the relevant standards administered by the3GPP (RTM) body and also described in many books on the subject, forexample, Holma H. and Toskala A [1]. It will be appreciated thatoperational aspects of the telecommunications network which are notspecifically described below may be implemented in accordance with anyknown techniques, for example according to the relevant standards orvariations thereof.

The network 100 includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices104. Data is transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Data istransmitted from terminal devices 104 to the base stations 101 via aradio uplink. The core network 102 routes data to and from the terminaldevices 104 via the respective base stations 101 and provides functionssuch as authentication, mobility management, charging and so on.Terminal devices may also be referred to as mobile stations, userequipment (UE), user terminal, mobile radio, and so forth. Base stationsmay also be referred to as transceiver stations/nodeBs/e-nodeBs, and soforth.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division modulation (OFDM) based interface for theradio downlink (so-called OFDMA) and a single carrier frequency divisionmultiple access scheme (SC-FDMA) on the radio uplink.

FIG. 2 shows a schematic diagram illustrating an OFDM based LTE downlinkradio frame 201. The LTE downlink radio frame is transmitted from a LTEbase station (known as an enhanced Node B) and lasts 10 ms. The downlinkradio frame comprises ten subframes, each subframe lasting 1 ms. Aprimary synchronisation signal (PSS) and a secondary synchronisationsignal (SSS) are transmitted in the first and sixth subframes of the LTEframe. A physical broadcast channel (PBCH) is transmitted in the firstsubframe of the LTE frame.

FIG. 3 is a schematic diagram of a grid which illustrates the structureof an example conventional downlink LTE subframe. The subframe comprisesa predetermined number of symbols which are transmitted over a 1 msperiod. Each symbol comprises a predetermined number of orthogonalsubcarriers distributed across the bandwidth of the downlink radiocarrier.

The example subframe shown in FIG. 3 comprises 14 symbols and 1200subcarriers spread across a 20 MHz bandwidth and in this example is thefirst subframe in a frame (hence it contains PBCH). The smallestallocation of physical resource for transmission in LTE is a resourceblock comprising twelve subcarriers transmitted over one subframe. Forclarity, in FIG. 3, each individual resource element is not shown,instead each individual box in the subframe grid corresponds to twelvesubcarriers transmitted on one symbol.

FIG. 3 shows in hatching resource allocations for four LTE terminals340, 341, 342, 343. For example, the resource allocation 342 for a firstLTE terminal (UE 1) extends over five blocks of twelve subcarriers (i.e.60 subcarriers), the resource allocation 343 for a second LTE terminal(UE2) extends over six blocks of twelve subcarriers (i.e. 72subcarriers), and so on.

Control channel data can be transmitted in a control region 300(indicated by dotted-shading in FIG. 3) of the subframe comprising thefirst “n” symbols of the subframe where “n” can vary between one andthree symbols for channel bandwidths of 3 MHz or greater and where “n”can vary between two and four symbols for a channel bandwidth of 1.4MHz. For the sake of providing a concrete example, the followingdescription relates to host carriers with a channel bandwidth of 3 MHzor greater so the maximum value of “n” will be 3 (as in the example ofFIG. 3). The data transmitted in the control region 300 includes datatransmitted on the physical downlink control channel (PDCCH), thephysical control format indicator channel (PCFICH) and the physical HARQindicator channel (PHICH). These channels transmit physical layercontrol information. Control channel data can also or alternatively betransmitted in a second region of the subframe comprising a number ofsubcarriers for a time substantially equivalent to the duration of thesubframe, or substantially equivalent to the duration of the subframeremaining after the “n” symbols. The data transmitted in this secondregion is transmitted on the enhanced physical downlink control channel(EPDCCH). This channel transmits physical layer control informationwhich may be in addition to that transmitted on other physical layercontrol channels.

PDCCH and EPDCCH contain control data indicating which subcarriers ofthe subframe have been allocated by a base station to specific terminals(or all terminals or subset of terminals). This may be referred to asphysical-layer control signalling/data. Thus, the PDCCH and/or EPDCCHdata transmitted in the control region 300 of the subframe shown in FIG.3 would indicate that UE1 has been allocated the block of resourcesidentified by reference numeral 342, that UE2 has been allocated theblock of resources identified by reference numeral 343, and so on.

PCFICH contains control data indicating the size of the control region(i.e. between one and three symbols for channel bandwidths of 3 MHz orgreater and between two and four symbols for channel bandwidths of 1.4MHz).

PHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

Symbols in a central band 310 of the time-frequency resource grid areused for the transmission of information including the primarysynchronisation signal (PSS), the secondary synchronisation signal (SSS)and the physical broadcast channel (PBCH). This central band 310 istypically 72 subcarriers wide (corresponding to a transmission bandwidthof 1.08 MHz). The PSS and SSS are synchronisation signals that oncedetected allow a LTE terminal device to achieve frame synchronisationand determine the physical layer cell identity of the enhanced Node Btransmitting the downlink signal. The PBCH carries information about thecell, comprising a master information block (MIB) that includesparameters that LTE terminals use to properly access the cell. Datatransmitted to terminals on the physical downlink shared channel(PDSCH), which may also be referred to as a downlink data channel, canbe transmitted in other resource elements of the subframe. In generalPDSCH conveys a combination of user-plane data and non-physical layercontrol-plane data (such as Radio Resource Control (RRC) and Non AccessStratum (NAS) signalling). The user-plane data and non-physical layercontrol-plane data conveyed on PDSCH may be referred to as higher layerdata (i.e. data associated with a layer higher than the physical layer).

FIG. 3 also shows a region of PDSCH containing system information andextending over a bandwidth of R344. A conventional LTE subframe willalso include reference signals which are discussed further below but notshown in FIG. 3 in the interests of clarity.

The number of subcarriers in a LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 subcarriers contained within a 20 MHz channel bandwidth (asschematically shown in FIG. 3). As is known in the art, data transmittedon the PDCCH, PCFICH and PHICH is typically distributed on thesubcarriers across the entire bandwidth of the subframe to provide forfrequency diversity.

FIG. 4 is a schematic diagram which illustrates some aspects of thestructure of an example conventional uplink LTE subframe. In LTEnetworks the uplink wireless access interface is based upon a singlecarrier frequency division multiple access (SC-FDMA) interface anddownlink and uplink wireless access interfaces may be provided byfrequency division duplexing (FDD) or time division duplexing (TDD),where in TDD implementations subframes switch between uplink anddownlink subframes in accordance with predefined patterns an in FDDimplementations the uplink and downlink channels are separated byfrequency. Regardless of the form of duplexing used, a common uplinkframe structure is utilised. The simplified representation of FIG. 4illustrates such an uplink frame at different levels of resolution witha frame of the uplink frame structure represented at the bottom of thefigure, a subframe represented in the middle of the figure, and a slotrepresented at the top of the figure. Thus the frame 400 is divided into 10 subframes 401 of 1 ms duration where each subframe 401 comprisestwo slots 402 of 0.5 ms duration. Each slot is then formed from sevenOFDM symbols 403 (numbered 0 to 6 in FIG. 4) where a cyclic prefix 404is inserted between each symbol. In FIG. 4 a normal cyclic prefix isused and therefore there are seven OFDM symbols within a subframe,however, if an extended cyclic prefix were to be used, each slot wouldcontain only six OFDM symbols. The resources of the uplink subframes arealso divided into resource blocks and resource elements in a broadlysimilar manner to downlink subframes.

As is well known, each uplink subframe may include a plurality ofdifferent channels, for example a physical uplink shared channel (PUSCH)405, a physical uplink control channel (PUCCH) 406, which may takevarious formats, and a physical random access channel (PRACH). Thephysical Uplink Control Channel (PUCCH) may carry control informationsuch as ACK/NACK to the base station for downlink transmissions,scheduling request indicators (SRI) for terminal devices wishing to bescheduled uplink resources, and feedback of downlink channel stateinformation (CSI) for example. The PUSCH may carry terminal deviceuplink data or some uplink control data. Resources of the PUSCH aregranted via PDCCH, such a grant being typically triggered bycommunicating to the network the amount of data ready to be transmittedin a buffer at the terminal device. The PRACH may be scheduled in any ofthe resources of an uplink frame in accordance with one of a pluralityof PRACH patterns that may be signalled to terminal device in downlinksignalling such as system information blocks. As well as physical uplinkchannels, uplink subframes may also include reference signals. Forexample, demodulation reference signals (DMRS) 407 and soundingreference signals (SRS) 408 may be present in an uplink subframe wherethe DMRS occupy the fourth symbol of a slot in which PUSCH istransmitted and are used for decoding of PUCCH and PUSCH data, and whereSRS are used for uplink channel estimation at the base station. Furtherinformation on the structure and functioning of the physical channels ofLTE systems can be found in reference [1].

In an analogous manner to the resources of the PDSCH for downlinkcommunications, resources of the PUSCH for uplink communications arescheduled or granted by the serving base station. Thus for data is to betransmitted by a terminal device, resources of the PUSCH are granted tothe terminal device by the base station. At a terminal device, PUSCHresource allocation is achieved by the transmission of a schedulingrequest or a buffer status report to its serving base station. Thescheduling request may be made, when there is insufficient uplinkresource for the terminal device to send a buffer status report, via thetransmission of Uplink Control Information (UCI) on the PUCCH when thereis no existing PUSCH allocation for the terminal device, or bytransmission directly on the PUSCH when there is an existing PUSCHallocation for the terminal device. In response to a scheduling request,the base station is configured to allocate a portion of the PUSCHresource to the requesting terminal device sufficient for transferring abuffer status report and then inform the terminal device of the bufferstatus report resource allocation via a DCI in the PDCCH.

Although similar in overall structure to downlink subframes, uplinksubframes have a different control structure to downlink subframes, inparticular an upper region 409 and a lower region 410 ofsubcarriers/frequencies/resource blocks of an uplink subframe arereserved for control signalling (as opposed to the initial symbols for adownlink subframe). Furthermore, although the resource allocationprocedure for the downlink and uplink are similar, the actual structureof the resources that may be allocated may vary due to the differentcharacteristics of the OFDM and SC-FDMA interfaces used in the downlinkand uplink respectively. For example, for OFDM each subcarrier may beindividually modulated and therefore it is not particularly significantwhether frequency/subcarrier allocations are contiguous. However, forSC-FDMA the subcarriers are modulated in combination and therefore itcan be more efficient to allocate contiguous frequency allocations foreach terminal device.

As a result of the above described wireless interface structure andoperation, one or more terminal devices may communicate data with oneanother via a coordinating base station, thus forming a conventionalcellular telecommunications system. However, as noted above, there arealso approaches for additionally allowing terminal devices tocommunicate directly with one another (i.e. without communicationspassing through a coordinating base station) using so-calleddevice-to-device (D2D) modes of operation. As explained further below,it is expected that in at least some modes of D2D operation a subset ofa network's radio resources will be reserved for D2D communications.Certain embodiments of the disclosure provide schemes for helping toestablish an appropriate amount of radio resources to reserve for D2Dcommunications in a wireless telecommunications system having regard toan amount of D2D communications (e.g. based on a measured/predictedcharacteristic of D2D traffic.

FIG. 5 schematically shows a telecommunications system 500 according toan embodiment of the disclosure. The telecommunications system 500 inthis example is based broadly on a LTE-type architecture withmodifications to support device-to-device communications (i.e. directsignalling exchange between terminal devices to communicate data betweenthem) generally in accordance with previously proposed schemes for D2Dcommunications. As such many aspects of the operation of thetelecommunications system 500 are already known and understood and notdescribed here in detail in the interest of brevity. Operational aspectsof the telecommunications system 500 which are not specificallydescribed herein may be implemented in accordance with any knowntechniques, for example according to the established LTE-standards andknown variations and modifications thereof (e.g. to provide/introducesupport for D2D communications).

The telecommunications system 500 comprises a core network part (evolvedpacket core) 502 coupled to a radio network part. The radio network partcomprises a base station (evolved-nodeB) 504, a first terminal device506 and a second terminal device 508. It will of course be appreciatedthat in practice the radio network part may comprise a plurality of basestations serving a larger number of terminal devices across variouscommunication cells. However, only a single base station and twoterminal devices are shown in FIG. 5 in the interests of simplicity.

As with a conventional mobile radio network, the terminal devices 506,508 are arranged to communicate data to and from the base station(transceiver station) 504. The base station is in turn communicativelyconnected to a serving gateway, S-GW, (not shown) in the core networkpart which is arranged to perform routing and management of mobilecommunications services to the terminal devices in thetelecommunications system 500 via the base station 504. In order tomaintain mobility management and connectivity, the core network part 502also includes a mobility management entity (not shown) which manages theenhanced packet service, EPS, connections with the terminal devices 506,508 operating in the communications system based on subscriberinformation stored in a home subscriber server, HSS. Other networkcomponents in the core network (also not shown for simplicity) include apolicy charging and resource function, PCRF, and a packet data networkgateway, PDN-GW, which provides a connection from the core network part502 to an external packet data network, for example the Internet. Asnoted above, the operation of the various elements of the communicationssystem 500 shown in FIG. 5 may be broadly conventional apart from wheremodified to provide functionality in accordance with embodiments of thedisclosure as discussed herein.

The first and second terminal devices 506, 508 are D2D enabled devicesconfigured to operate in accordance with embodiments of the presentdisclosure as described herein. The terminal devices 506, 508 eachcomprise a transceiver unit 506 a, 508 a for transmission and receptionof wireless signals and a controller unit 506 b, 508 b configured tocontrol the respective terminal devices 506, 508. The respectivecontroller units 506 b, 508 b may each comprise a processor unit whichis suitably configured/programmed to provide the desired functionalityusing conventional programming/configuration techniques for equipment inwireless telecommunications systems. The respective transceiver units506 a, 508 a and controller units 506 b, 508 b are schematically shownin FIG. 5 as separate elements. However, it will be appreciated for eachof the terminal devices the functionality of the terminal devicesreceiver and controller units can be provided in various different ways,for example using a single suitably programmed general purpose computer,or suitably configured application-specific integratedcircuit(s)/circuitry. It will be appreciated the first and secondterminal devices 506, 508 will in general comprise various otherelements associated with their operating functionality in accordancewith established wireless telecommunications techniques (e.g. a powersource, possibly a user interface, and so forth).

The base station 504 is configured to support D2D communications betweenterminal devices in accordance with embodiments of the presentdisclosure as described herein. The base station 504 comprises atransceiver unit 504 a for transmission and reception of wirelesssignals and a controller unit 504 b configured to control the basestation 504. The controller unit 504 b may comprise a processor unitwhich is suitably configured/programmed to provide the desiredfunctionality using conventional programming/configuration techniquesfor equipment in wireless telecommunications systems. The transceiverunit 504 a and the controller unit 504 b are schematically shown in FIG.5 as separate elements for ease of representation. However, it will beappreciated that the functionality of these units can be provided invarious different ways, for example using a single suitably programmedgeneral purpose computer, or suitably configured application-specificintegrated circuit(s)/circuitry or using a plurality of discretecircuitry/processing elements for providing different elements of thedesired functionality. It will be appreciated the base station 504 willin general comprise various other elements associated with its operatingfunctionality. For example, the base station 504 will in generalcomprise a scheduling entity responsible for scheduling communications.The functionality of the scheduling entity may, for example, be subsumedby the controller unit 504 b.

Thus, the base station 504 is configured to communicate data with thefirst terminal device 506 over a first radio communication link 510 andcommunicate data with the second terminal device 508 over a second radiocommunication link 512. Both radio links may be supported within asingle radio frame structure associated with the base station 504. It isassumed here the base station 504 is configured to communicate with theterminal devices 506, 508 over the respective radio communication links510, 512 generally in accordance with the established principles ofLTE-based communications.

However, in addition to the terminal devices 506, 508 being arranged tocommunicate data to and from the base station (transceiver station) 504over the respective first and second radio communication links 510, 512,the terminal devices are further arranged to communicate with oneanother (and other terminal devices within the wirelesstelecommunications system) in a device-to-device (D2D) manner over a D2Dradio communication link 514, as schematically indicated in the figure.The underlying principles of the D2D communications supported in thewireless telecommunications system of FIG. 5 may follow any previouslyproposed techniques, but with modifications to support approaches inaccordance with embodiments of the disclosure as described herein.

There are a number of possible approaches to the implementation of D2Dcommunications within an LTE-based wireless telecommunications systemthat have been proposed for different scenarios.

Some approaches may rely on a coordinating entity, such as a basestation or other network entity, to allocate specific transmissionresources for use by respective terminal devices to transmit data. Forexample, resources within the wireless access interface provided forcommunications between terminal devices and a base station may be usedfor D2D communications and a base station may allocate resources forspecific D2D communications.

That is to say, the base station may be responsible for scheduling whichterminal devices transmit D2D communications on which resources in abroadly similar manner to the way in which the base station isresponsible for scheduling conventional uplink communications. Thusterminal devices may receive control signalling from the base station toindicate which resources they should use for transmitting user data toanother terminal device in a D2D manner. This type of approach maygenerally be referred to as a Mode 1 approach.

Other approaches may not rely on any coordinating entity for managingaccess to radio resources by terminal devices undertaking D2Dcommunications. For example it has been proposed in document R2-133840[2] to use a Carrier Sense Multiple Access, CSMA, approach to provide adegree of co-ordination for D2D transmissions by terminal devicesthrough contention based scheduling by each terminal device. In effecteach terminal device first listens to identify which resources arecurrently being used, and then schedules its own transmissions on unusedresources. This type of approach may generally be referred to as a Mode2 approach.

Thus, in some respects, a Mode 1 approach may be seen as an approach inwhich access to resources for D2D communications is scheduled by acoordinating entity whereas a Mode 2 approach may be seen as an approachin which access to resources for D2D communications are not scheduled bya coordinating entity and are contention based.

Some proposed arrangements include those in which a terminal device actsas a controlling entity for a group of terminal devices to co-ordinatetransmissions of the other members of the group. Examples of suchproposals are provided in the following disclosures:

-   [3] R2-133990, Network control for Public Safety D2D Communications;    Orange, Huawei, HiSilicon, Telecom Italia-   [4] R2-134246, The Synchronizing Central Node for Out of Coverage    D2D Communication; General Dynamics Broadband UK-   [5] R2-134426, Medium Access for D2D communication; LG Electronics    Inc

In some respects these approaches may be seen as variations of a Mode 1approach in which a “master” terminal device plays a role correspondingto that of a base station in allocating (scheduling) D2D resources amongterminal devices wishing make D2D communications.

In other arrangements one of the terminal devices of a group may firstsend a scheduling assignment, and then transmit data without a centralscheduling terminal device or controlling entity controlling thetransmissions. The following disclosures provide examples of thisde-centralised arrangement:

-   [6] R2-134238, D2D Scheduling Procedure; Ericsson;-   [7] R2-134248, Possible mechanisms for resource selection in    connectionless D2D voice communication; General Dynamics Broadband    UK;-   [8] R2-134431, Simulation results for D2D voice services using    connectionless approach, General Dynamics Broadband UK

In particular, the last two disclosures listed above, R2-134248 [7],R2-134431 [8], disclose the use of a scheduling channel, used byterminal devices to indicate their intention to schedule data along withthe resources that will be used. The other disclosure, R2-134238 [6],does not use a scheduling channel as such, but deploys at least somepredefined resources to send the scheduling assignments. Theseapproaches may be seen as Mode 2 type approaches.

Other example arrangements disclosed in [9] and [10] require a basestation to provide feedback to the communications devices to controltheir transmissions. Document [11] discloses an arrangement in which adedicated resource exchanging channel is provided between cellular userequipment and device-to-device user equipment for interference controland resource coordination.

It is to be expected that device-to-device communications whenimplemented in the context of an existing LTE-based wirelesstelecommunications network will use transmission resources associatedwithin the existing LTE radio interface. In particular, it is expectedthat device-to-device communications will use radio resources fromwithin the existing LTE uplink frame structure. There are variousreasons for this. For example, traffic profiles in wirelesstelecommunications systems are typically such that an uplink channel ismore likely to have more spare capacity then a downlink channel.Furthermore, the downlink channel is associated with more powerfultransmissions from a base station and these are more likely to swamp andinterfere with device-to-device communications.

One factor that is expected to be significant in determining the mannerin which terminal devices undertake D2D communications is the extent towhich the terminal devices are within network coverage. For example,terminal devices which are outside network coverage may be expected tooperate according to Mode 2 in the absence of any coordinatinginformation from a base station (although such terminal device couldoperate in accordance with Mode 1 with a terminal device taking on therole of centralised scheduling/coordination). Terminal devices withinnetwork coverage might be expected to operate according to Mode 1, sincecentralised control will generally provide improved performance (examplewith reduced contention). Furthermore, in some circumstances there maybe terminal devices undertaking D2D communications while they are in anarea of poor coverage, for example at a cell edge. In this respect theterminal devices may be able to receive some communications from thebase station, for example system information broadcasts, but may not beable to reliably receive other routine communications, for exampleresource allocation signalling. In this scenario the terminal devicesmay operate according to Mode 2, but nonetheless receive someconfiguration information from the base station regarding the overallresources available for supporting D2D communications in the wirelesstelecommunications system.

It is expected that D2D communications within a cell served by a basestation will be restricted to a subset of transmission resources (interms of times and/or frequency) selected from the overall range oftransmission resources available in the cell. For example, if a basestation in a cell is configured to operate over a 20 MHz bandwidth LTEradio subframe (e.g. for supporting uplink communications across theradio communication links 510, 512 represented in FIG. 5), it isexpected that D2D communications between the terminal devices will berestricted to a pool of resources taken from within the cell's overalltransmission resources. Furthermore, it is expected for someimplementations the pool of transmission resources to be used forsupporting D2D communications (e.g. the radio communication link 514 inFIG. 5) will not be available for supporting conventionaluplink/downlink signalling (e.g. the radio communication links 510, 512in FIG. 5). In this regard the set (pool) of resources to be madeavailable for supporting D2D communications may be considered as beingreserved for D2D communications.

Thus to summarise, a portion of the transmission resources (e.g. one ormore blocks of time and/or frequency) that would otherwise be availablefor communications between the base station and terminal devices in asystem which did not support D2D communications may be reserved forcommunications between terminal devices in a wireless telecommunicationssystem which does support D2D communications. The specific resourcesreserved for D2D communications in terms of time and frequency resourcesmay come from the base station's conventional uplink or downlinkresources. However, as noted above, it is more likely to come from theuplink resources. Furthermore, the manner in which the resources arespread throughout the communication cell's overall operating bandwidthmay be different in different implementations. In some cases the pool ofresources reserved for D2D communications may be contiguous in time andfrequency (e.g. corresponding to a continuous band of resources within aframe structure such as represented in FIG. 4, for example). In othercases the pool of resources for supporting D2D communications may benon-contiguous in time and/or frequency. For example, in oneimplementation the transmission resources reserved for D2Dcommunications may comprise a continuous band of frequencies within theoverall cell bandwidth, but D2D communications may not be available inevery (sub)frame. In another example, the D2D communications may besupported in every subframe, but may use non-contiguous frequencies.More generally, once an amount of resources to reserve for D2D operationhas been established in accordance with the principles described herein,the specific arrangement of the transmission resources in terms of timesand frequencies that are reserved is not significant. Furthermore, thenature of the physical layer signalling and protocols adopted for D2Dcommunications between terminal devices using the D2D pool oftransmission resources is also not significant to the principles ofoperation described herein. For example, D2D communications may be basedon blocks of time and frequency corresponding to those used in aconventional LTE system, or a different system may be used.

However, as noted above, the inventors have recognised one issue forconsideration for D2D communications is how much radio resource shouldbe reserved for supporting D2D communications in a wirelesstelecommunications network. If a pool is too small, there will be anincreased risk of congestion/collision. However if a resource pool istoo large, it may represent an under-utilised (i.e. wasted) portion oftransmission resources that might otherwise be used for conventionalnon-D2D communications.

With this in mind, there is proposed an approach for dynamicallyadapting the amount of resources available for D2D communications in awireless telecommunications system. In broad summary a network entity,for example a base station, may be responsible for establishing a set ofresources to be available for D2D communications and convey anindication of this to terminal devices operating in the system. Thenetwork entity may then obtain information regarding the extent to whichthe resources that are currently set aside for D2D communications arebeing used, i.e. the network entity may obtain information regarding thedegree of utilisation of the resources currently made available for D2Dcommunications. If the network entity determines the D2D resources arebeing under-utilised (e.g. with a fractional utilisation less than alower threshold amount, for example lower than 0.7, 0.6, 0.5, 0.4 or0.3, or lower), it may reduce the amount of resources reserved for D2Doperations (and communicate this to the terminal devices accordingly).This frees up a portion of the resources previously reserved for D2Dcommunications for non-D2D traffic. If, on the other hand, the networkentity determines the D2D resources are being over-utilised (e.g. with afractional utilisation greater than an upper threshold amount, forexample higher than 0.5, 0.6, 0.7, 0.8 or 0.9, or more), it may increasethe amount of resources reserved for D2D operations (and communicatethis to the terminal devices accordingly). This can help reduce the riskof D2D traffic congestion.

There are various different ways in which a network entity, for examplethe base station 504 represented in FIG. 5, can obtain informationregarding the extent to which transmission resources set aside for D2Doperation are being utilised to allow it to respond by changing theamount of resources allocated for D2D operation, as now described.

FIG. 6 is a ladder diagram schematically representing signallingexchange between the base station 504, and the terminal devices 506, 508schematically represented in FIG. 5 in accordance with certainembodiments of the disclosure. It is assumed here for the sake ofexample the terminal devices 506, 508 are exchanging D2D communications,with the terminal device 506 transmitting and the terminal device 508receiving. In this regard the terminal device 506 may be referred to asthe transmitting terminal device (UE “T”) while the terminal device 508may be referred to as the receiving terminal device (UE “R”).

In step S1 the base station 504 establishes an initial D2D resourcepool. This is a set of transmission resources which are to be madeavailable/reserved for D2D operation. This step may be performed inresponse to the base station undergoing a switch on or reset procedurein respect of its support for D2D communications. The initial size ofthe D2D resource pool established in step S1 and the manner in which itis determined is not overly significant. For example, the initial D2Dresource pool established in step S1 may correspond with a predefinedset of transmission resources.

In step S2 the base station transmits an indication of the set ofresources comprising the D2D transmission resource pool established instep S1 to the terminal devices. This information may, for example, betransmitted in accordance with established techniques for communicatingconfiguration information in wireless telecommunications systems, forexample through system information block (SIB) signalling in anLTE-based network. As schematically indicated in FIG. 6, both thetransmitting terminal device 506 and the receiving terminal device 508receive this information. Generally speaking, terminal devices which areto make D2D transmissions in accordance with Mode 2 operations acquirethis information to allow them to select transmission resources fortheir transmissions. However, terminal devices which may receive D2Dtransmissions but do not expect to make D2D transmissions maynonetheless also acquire this information so they determine whatresources to monitor for D2D transmissions addressed to them (thisapplies for both Mode 1 and Mode 2 operation).

Thus, at the end of step S2, a D2D resource pool has been establishedand communicated to the terminal devices 506, 508.

In step S3 the transmitting terminal device 506 identifies that it hasdata to transmit to the receiving terminal device 508 in a D2D mode. Forthe sake of example, it is assumed here the transmitting terminal deviceand the receiving terminal device support a “walkie-talkie” mode, andstep S3 corresponds with a user of the transmitting terminal device 506pressing a button to indicate they are about to begin talking to a userof the receiving terminal device 508 (and potentially other terminaldevices in a broadcast walkie-talkie mode). However, it will beappreciated the exact nature of the data to be transmitted the triggerfor transmission are not significant.

In step S4 the transmitting terminal device seeks to access resourceswithin the set of transmission resources set aside for D2Dcommunications (the D2D pool). The exact mechanism and protocols used todo this will depend on the specific D2D implementation at hand. Forexample, any of the known approaches discussed above may be adopted, forexample a “wait and listen”/CSMA type approach may be used.

If in step S4 the transmitting terminal device is able to accesstransmission resources in the D2D pool (i.e. there are resourcesavailable for use by the transmitting terminal device), processing mayproceed to step S9, where the D2D communications between thetransmitting terminal device 506 and the receiving terminal device 508may proceed in accordance with whichever D2D protocols are adopted forthe implementation at hand.

However, if in step S4 the transmitting terminal device identifies thatit has faced a restriction in its attempts to access (or at least claimaccess to) transmission resources within the D2D resource pool, forexample because all the D2D resources are already allocated for use byother terminal devices such that the transmitting terminal device cannotaccess any transmission resources, processing proceeds to step S5.

In step S5 the transmitting terminal device transmits a report to thebase station indicating it has had difficulty accessing the transmissionresources within the D2D pool. This signalling may be exchanged inaccordance with conventional reporting techniques, for example usingradio resource control, RRC, signalling techniques. The exact nature ofthe report is not significant. For example, the report may simply conveyan indication the terminal device 506 has tried and failed to make a D2Dtransmission because there were insufficient resources available. Insome examples the indication the transmitting terminal device's attemptto access the transmission resources within the D2D pool was in some wayrestricted may be communicated to the base station in association with aconnections establishment procedure, for example in association withConnection Setup Complete signalling. In some example implementations,certain aspects of report signalling of the kind represented in step S5may be configured through system information signalling.

The signalling exchanged step S5 in effect corresponds to the basestation receiving a feedback report from the terminal device indicatingthe extent to which the D2D resource pool is currently (or at least atthe time of S4) being utilised. In this example where the terminaldevice 506 transmits the signalling in step S5 in response to a failureto access any transmission resources, the indication is in effect anindication of 100% utilisation for the D2D resource pool, at least inthe vicinity of the transmitting terminal device.

In step S6 the base station responds to the feedback indicating theresource pool is over-utilised by establishing an updated resource poolcomprising more transmission resources. For example, in oneimplementation it may be established that an optimum level ofutilisation is 70% (0.7 fractional utilisation), and so the base stationmay increase the size of the D2D resource pool (i.e. the amount oftransmission resources to be set aside for D2D communications) by anamount the order of 1/0.7 (i.e. 1.4). However, the exact extent to whichthe resource pool is increased will be a matter of implementation. Forexample, in a wireless telecommunications system where there is expectedto be only steady and slow changes in the extent to which the D2Dcommunications are utilised, a relatively low increase may be consideredappropriate, for example 10% or 20%, in the expectation that it isunlikely the new larger resource pool will itself rapidly becomeover-utilised. However, in a wireless telecommunication system in whichthere is expected to be a greater degree of variation in D2Dutilisation, a larger increase may be considered appropriate to morereadily accommodate peaks in D2D communications.

In Step S7, and in a manner similar to step S2, the base stationtransmits an indication of the updated set of resources comprising theD2D transmission resource pool established in step S6 to the terminaldevices. Again, this information may be transmitted in accordance withany established techniques for communicating configuration informationin wireless telecommunications systems, such as system informationsignalling.

Thus, at the end of step S7, an updated D2D resource pool has beenestablished and communicated to the terminal devices 506, 508.

On receiving the updated D2D resource pool in step S7, the receivingterminal device 508 begins monitoring the updated D2D resources forpotential transmissions, whereas prior to this it will have monitoredthe set of resources comprising the previously determined set ofresources (established in step S1).

On receiving the updated D2D resource pool in step S7, the transmittingterminal device 506 in effect returns to step S4 where it attempts togain to access to resources from the (now updated) D2D resource pool tomake its transmission to the receiving terminal device 508. If thetransmitting terminal device is successful in claiming access toresources from the newly-updated D2D resource pool, processing proceedto step S9. In step S9 the D2D communications can take place using therelevant resources from the D2D resource pool in accordance withwhichever D2D protocols are adopted for the implementation at hand.However, if the transmitting terminal device 506 again fails to identifytransmission resources available for it to use within the D2D pool,processing may proceed to step S5 and so on as discussed above.

After sending the utilisation report in step S5, and before receivingthe indication of the updated D2D resource pool in step S7, the terminaldevice 506 might make further attempts to access resources within theoriginal D2D resource pool, for example, in association with a back-offtimer, since resources may become available in the meantime.Furthermore, the transmitting terminal device 506 might attempt toobtain resources to communicate with the receiving terminal device inanother manner, for example by requesting the base station allocatespecific resources for it to use (i.e. in effect switching to Mode 1operation), or attempting to use an alternate D2D resource pool if oneis available.

It will be appreciated the approach of FIG. 6 will generally beperformed in an iterative manner, and the description above has focusedonly on an initial iteration. That is to say, processing represented inFIG. 6 may in effect be continuously looped through in respect of allterminal devices seeking to make D2D transmissions in the wirelesscommunication system.

Thus, FIG. 6 represents one mechanism whereby a base station may monitorthe degree of utilisation of a D2D resource pool and adjust the size ofthe pool according to current utilisation. In some respects the approachof FIG. 6 is relatively coarse in providing a broadly binary indicationof utilisation. That is to say, if the base station receives anover-utilisation report from a terminal device, it is made aware therehas been an occurrence of 100% utilisation, whereas if the base stationdoes not receive an over-utilisation report, it is made aware is not anoccurrence of 100% utilisation, but the base station may not be aware ofwhat utilisation is.

It will be appreciated the approach of FIG. 6 can be subject to variousmodifications. For example, in the approach described above, thetransmitting terminal device 506 identified it was restricted fromaccessing resources in the D2D pool in step S4 by virtue of no resourcesbeing available so that its transmission failed. In other examples, thetransmitting terminal device may successfully make its transmission, butdetermine that it was nonetheless restricted in some way, for examplebecause it had to wait for more than a threshold amount of time beforeresources became available, or it identified that only a small fractionof the available resources remained available for use. Thus, inaccordance with some examples the transmitting terminal device mayproceed to make its D2D transmission, but nonetheless provide a feedbackreport to the base station to indicate there was some degree ofrestriction (e.g. a delay greater than a threshold duration, or lessthan a predefined threshold amount of resources remaining available forselection).

It will also be appreciated the manner in which the base stationdetermines whether and how to establish an updated D2D resource pool maybe different for different implementations. For example, in some casesthe base station may react immediately to receiving an indication ofover-utilisation, whereas in other cases the base station may wait toreceive a number of indications of over-utilisation within a given timeperiod before responding. That is to say, the base station may not reactto a single isolated instance of over-utilisation, and may insteadrequire multiple over-utilization reports from the same and/or fromdifferent terminal devices before reacting. Furthermore, in accordancewith some examples of the approach represented in FIG. 6 there may be noready mechanism provided for the base station to determine if the D2Dresource pool is significantly under-utilised. Therefore, if there is aperiod of time greater than a predefined threshold during which the basestation has not received any over-utilisation reports, the base stationmay proceed to reduce the size of the D2D resource pool (and inform theterminal devices accordingly), and continue doing this until anover-utilisation report is received. The base station may increase theD2D resource pool (e.g. in a step corresponding to step S6 in FIG. 6),and reset the timer for determining when it will again start to tryreducing the size of the D2D pool in the absence of any over-utilisationreports.

FIG. 7 is a ladder diagram schematically representing signallingexchange between the base station 504, and the terminal devices 506, 508schematically represented in FIG. 5 in accordance with certain otherembodiments of the disclosure. Various aspects of FIG. 7 are similar to,and will be understood from, corresponding aspects of FIG. 6 and are notdescribed again in detail in the interests of brevity.

In step U1 the base station 504 establishes an initial D2D resourcepool. This step corresponds with step U1 in FIG. 6.

In step U2 the base station transmits an indication of the set ofresources comprising the D2D transmission resource pool established instep U1 to the terminal devices 506, 508. This step corresponds withstep S2 in FIG. 6.

Thus, at the end of step U2, an initial D2D resource pool has beenestablished and communicated to the terminal devices 506, 508.

It is assumed in this example the transmitting terminal device in facthas no difficulty accessing D2D resources from the available pool forcommunicating with the receiving terminal device in a D2D mode, and itproceeds to undertake D2D transmissions to the receiving terminal devicein accordance with whichever D2D protocols are being implemented. Thisis schematically presented by step U3 in FIG. 7.

As schematically represented by step U4 in FIG. 7, the approach of FIG.7 differs from that of FIG. 6 in that the base station 504 is configuredto directly monitor utilisation of the D2D resource pool. The basestation may do this, for example, by monitoring for transmissions beingmade on the reserved D2D resources, for example by monitoring forsignalling signatures associated with D2D transmissions on the relevantresources, or simply measuring the power being transmitted in the cellon the relevant resources. The utilisation monitoring in step U4 thusprovides the base station with an indication of the extent to which theD2D resources are being utilised.

In step U5 the base station establishes an updated D2D resource pool bytaking account of the extent of D2D resource utilisation determined fromthe monitoring in step U4.

For example, the base station may be configured to seek to maintain apre-defined fractional utilisation, such as somewhere between 60% and80% (the desired fractional utilisation in any given implementation willtypically depend on the extent of variation which is expected to occuron timeframes faster than the rate at which the D2D resource pool willbe updated). To avoid overly frequent changes in the D2D resource pool,the base station may be configured to establish an updated D2D resourcepool only if (1) the measured fractional utilisation in step U4 exceedsan upper threshold that is larger than the desired fractionalutilisation, either instantaneously or for longer than a predefinedduration, or (2) the measured fractional utilisation in step U4 fallsbelow a lower threshold that is less than the desired fractionalutilisation, either instantaneously or for longer than a predefinedduration. In response to these conditions, the base station may increaseor decrease the D2D resource pool size accordingly.

It will be appreciated the exact procedures and algorithms to be appliedfor determining when and what changes to the D2D resource pool should bemade will depend on the application at hand. More generally, theoptimisation procedures may be implemented in accordance with any knowntechniques for resource optimisation. What is significance in accordancewith certain embodiments of the disclosure is the provision of schemesthat allow for dynamic D2D resource pool allocation in response to D2Dresource utilisation. The specific optimisation procedures adopted todefine how the system should react in any given situation are lesssignificant and will depend on the implementation at hand, for exampledepending on magnitudes and speed of expected variations in D2D traffic.

In Step U6, and in a manner similar to step U1, the base stationtransmits an indication of the updated set of resources comprising theD2D transmission resource pool established in step U5 to the terminaldevices (assuming there has been an update). Again, this information maybe transmitted in accordance with any established techniques forcommunicating configuration information in wireless telecommunicationssystems, such as system information signalling.

Thus, at the end of step U6, an updated D2D resource pool has beenestablished and communicated to the terminal devices 506, 508. Onreceiving the updated D2D resource pool in step U6, the various terminaldevices may begin monitoring the updated D2D resources for potentialtransmissions and may begin using the updated D2D resources for D2Dtransmissions.

Again it will be appreciated the approach of FIG. 7 will typically beincremented as an iterative approach, for example with the base stationconfigured to perform monitoring in accordance with step U4, andpotential resource pool updates in accordance with step U5, on anongoing periodic basis.

An advantage of the approach represented in FIG. 7 as compared to theapproach represented in FIG. 6 is the provision of a more refinedindication of the extent of D2D resource utilisation. For example, inthe example of FIG. 6 the base station is in effect provided with asimple binary indication of over-utilisation (i.e. over-utilisationsignalling received from a terminal device) or non-over-utilisation(i.e. no over-utilisation signalling received). The approach of FIG. 7allows a base station to generate a measure of actual utilisation,thereby allowing the base station to readily identify and react tosituations of under-utilisation, and also to the system approachingover-utilisation before terminal devices start being unable to make D2Dtransmissions. However, a potential drawback with the approach of FIG. 7in some situations is the possibility for the base station 504 to beunable to monitor all D2D transmissions occurring in its cell. Forexample, D2D transmissions between two closely spaced terminal devicesat cell edge may be made with insufficient power for the base station torecognise the transmission is occurring. This means there is thepotential for congestion that the base station does not recognise.Therefore a combination of the approaches of FIGS. 6 and 7 may bepreferred in some implementations. This allows the more refined feedbackfor adaption provided by the base station monitoring approachrepresented in FIG. 7 to be used in conjunction with the failsafeapproach of individual terminal devices being able to report if they areunable to make transmissions, as in FIG. 6.

FIG. 8 is a ladder diagram schematically representing signallingexchange between the base station 504, and the terminal devices 506, 508schematically represented in FIG. 5 in accordance with certain otherembodiments of the disclosure. FIG. 8 also represents a third terminaldevice 700 (labelled as UE “O”) and this may be referred to as the“other” terminal device 700 to distinguish it from the transmittingterminal device 506 and the receiving terminal device 508. The otherterminal device 700 is represented as an separate terminal device inFIG. 8 because its functionality as described herein may in general beprovided by any terminal device within the wireless telecommunicationssystem in the vicinity of the transmitting and receiving terminaldevices 506, 508. Thus, the other terminal device 700 may in factcorrespond with the transmitting terminal device 506, with the receivingterminal device 508, or with another terminal device altogether. Variousaspects of FIG. 8 are similar to, and will be understood from,corresponding aspects of FIGS. 6 and 7 and are not described again indetail in the interests of brevity.

In step T1 the base station 504 establishes an initial D2D resourcepool. This step corresponds with step S1 in FIG. 6 and step U1 in FIG.7.

In step T2 the base station transmits an indication of the set ofresources comprising the D2D transmission resource pool established instep T1 to the terminal devices. This step corresponds with step S2 inFIG. 6 and step U2 in FIG. 7. However, as schematically represented inFIG. 8, the other terminal device 700 also receives the indication ofthe D2D resource pool in step T1. Again, this information may becommunicated in accordance with established techniques for communicatingconfiguration information in wireless telecommunications systems, forexample through system information or other control signalling.

Thus, at the end of step T2 in FIG. 8, a D2D resource pool has beenestablished and communicated to the terminal devices 506, 508, 700.

As with FIG. 7, it is assumed for FIG. 8 the transmitting terminaldevice 506 has no difficulty accessing D2D resources from the availablepool for communicating with the receiving terminal device 508 in a D2Dmode. Thus the transmitting terminal device proceeds to undertake D2Dtransmissions to the receiving terminal device in accordance withwhichever D2D protocols are being implemented. This is schematicallypresented by step T3 in FIG. 8.

In step T4 of FIG. 8 the other terminal device 700 (which as noted abovemay in fact correspond with the transmitting or receiving terminaldevice) is configured to monitor utilisation of the D2D resource pool inits vicinity. The other terminal device 700 may do this, for example, bymonitoring for transmissions being made on the reserved D2D resources,for example by monitoring for signalling signatures associated with D2Dtransmissions on the relevant resources, or simply measuring the powerbeing transmitted in the cell on the relevant resources. The utilisationmonitoring in step T4 thus provides an indication of the extent to whichthe D2D resources are being utilised.

In step T5 the other terminal device 700 transmits a report to the basestation indicating the extent to which the D2D resources are beingutilised according to the monitoring measurements from step T4. Thisreport may, for example, comprise indications of the measurements made,or a simple indication of a fractional utilisation for the D2D resourcepool in the vicinity of the other terminal device derived from themeasurements. This signalling may be exchanged in accordance withconventional reporting techniques in wireless telecommunicationssystems, for example using radio resource control, RRC, signallingtechniques.

The signalling exchanged in step T5 in effect corresponds to the basestation receiving a feedback report from the terminal device indicatingthe extent to which the D2D resource pool is currently (or at least atthe time of T4) being utilised.

It will be recognised the combination of steps T4 and T5 in FIG. 8broadly correspond with step U4 in FIG. 7 in that they provide the basestation with an indication of measurements of resource utilisation.However, whereas in FIG. 7 these measurements are made by the basestation itself, in FIG. 8 the measurements are made by a terminal devicewhich is remote from the base station reported back to the base station.In effect the approach of FIG. 8 allows the base station to use one ormore terminal devices to remotely measure D2D utilisation on its behalf.

Once the base station has received (determined) the extent to which theradio resources made available for D2D transmissions are being utilisedin step T5, processing proceed to steps T6 and T7 which are similar to,and will be understood from steps U5 and U6 represented in FIG. 7.

Thus, at the end of step T7, an updated D2D resource pool has beenestablished and communicated to the terminal devices 506, 508, 700. Onreceiving the updated D2D resource pool in step T6, terminal devices maybegin monitoring the updated D2D resources for potential transmissionsand may begin using the updated D2D resources for D2D transmissions.Furthermore, terminal devices which are to perform monitoring of thekind represented in step T4 may proceed with monitor the updatedresource pool.

Thus, as noted above, the approach of FIG. 8 is similar to the approachof FIG. 7, but the base station in effect uses remote terminal devicesto establish measurements for D2D resource pool utilisation. In someexamples each and every terminal device may be configured to monitorutilisation of D2D resources in its own vicinity and report back to thebase station in steps corresponding to T4 and T5. In other examples onlya subset of terminal devices operating in the wirelesstelecommunications system may be configured to perform this function.For example, the base station may configure a subset of terminal devicesspread throughout the cell to perform this function to give the basestation an indication of the extent to which D2D resources are beingused (utilised) throughout the cell. For example, with this informationthe base station may in principle reserve different sets of resourcesfor different locations in a cell according to local utilisationreports.

Thus the approach of FIG. 8 provides similar advantages to thosediscussed above for FIG. 7, while also reducing the risk of there beinglocations within a cell where the D2D resources are over-utilised butthe base station is not made aware of this.

Terminal devices which are configured to provide reporting of the kindrepresented in step T5 may be configured to do this on request, forexample on receiving signalling from the base station to trigger theexecution of steps corresponding to steps T4 and T5 in FIG. 8 (forexample using Measurement Control and Measurement Report techniques inan LTE context), and/or may be configured to perform the monitoring andreporting according to a predefined the measurement schedule. In anotherexample, certain terminal devices may be configured to regularly monitorutilisation, but to only send a report if certain conditions are met,for example if the measured utilisation is departing from a desiredutilisation by more than a threshold amount.

Thus, approaches of the kind described above provide mechanisms forallowing a set of radio resources allocated for D2D communicationswithin a wireless communication system to be dynamically adjusted inresponse to utilisation. It will be appreciated that features of thedifferent approaches may be combined. For example, as well as havingterminal devices provide feedback on resource utilisation measurementsas in FIG. 8, the base station itself may also monitor utilisation as inFIG. 7, and/or furthermore may adopt the approach adopted in FIG. 6.

In some cases the responses to measured changes in D2D resourceutilisation may be relatively fast, for example a base station may beconfigured to update the D2D resource pool within a time frame on theorder of seconds or minutes. However, in other examples the approachesof the kind described herein may be used to establish a D2D trafficprofile on a more long-term basis. This may then form the basis for morelong-term reconfiguration. Also, rather than acting a reactive manner,the principles described above may be used to establish a predictedpattern of D2D resource usage with changes made accordingly. Forexample, in an approach based on FIG. 7, the base station may monitorutilisation of a D2D resource pool for an extended period, for example aweek, to determine a pattern of usage (e.g. times of day when D2Dcommunications are particularly high or low), and may then configureupdated D2D resources at different times according to this pattern. Thatis to say, there may in effect be a significant delay between steps U4and U5 in the processing represented in FIG. 7.

Whilst in the above-described examples it is a base station that isresponsible for establishing the pool (set) of resources to use for D2Dcommunications within a cell, and will be appreciated that in otherexamples, a relay node may perform this task. In other implementations adifferent network entity may be responsible for performing this task,for example on the basis of feedback reporting of the kind describedabove which is passed back to the network entity from a base station. Inthis regard the set of resources reserved for D2D communications may bedetermined on a cell-by cell basis, or more widely in the network. Forexample, a network entity may determine there should be a change in theresources reserved for D2D communications within a particular cellbecause of reported congestion or under-utilisation in that cell, andmay instruct a base station serving that cell to respond accordingly.The network entity may also instruct other base stations to adjust theresources they have reserved for D2D operations within their respectivecells. This may be done, for example, to ensure there is a degree ofuniformity in the resources reserved for D2D communications in differentcells within the network, for example among neighbouring cells.

Whilst in the above-described embodiments it is assumed the terminaldevices undertaking D2D communications are also able to communicate withother terminal devices via a base station in a conventional non-D2Dmanner, it will be appreciated that in principle a terminal deviceaccording to an embodiment of the disclosure could be a dedicated D2Ddevice that did undertake communications with other terminal devicesthrough a base station.

Although the above-described examples have focused on implementations inthe context of an LTE-based wireless telecommunications system, it willbe appreciated similar principles can be adopted for in wirelesstelecommunications systems operating in accordance with other protocols.

Thus there has been described schemes for supporting device-to-device,D2D, communications between terminal devices in a wirelesstelecommunication system. A network entity, e.g. a base station,establishes a set (pool) of radio resources to be reserved for use forD2D communications and communicates an indication of these resources toterminal devices. The terminal devices may then proceed to undertake D2Dcommunications using the reserved set of radio resources. On an ongoingbasis the network entity monitors the extent to which the set of radioresources reserved for D2D communications is being used, for examplebased on feedback received from terminal devices or its ownmeasurements. If it is determined the set of radio resources reservedfor D2D communications is being under-utilized or over-utilized, thenetwork entity may establish an updated set of radio resources to beused for D2D communications, and communicate this to the terminaldevices. For example, if the reserved resources are being under-utilizedby at least a predefined amount, the amount of resources set aside forD2D communications may be reduced. Conversely, if the reserved resourcesare being over-utilized, e.g. more than a predefined fractionalutilization, the set of resources may be increased. Thus a mechanism isprovided for dynamically adjusting the size of a set of resourcesavailable for D2D communications in response to changing resourceutilization. This can help with optimizing overall resource usage withinthe wireless telecommunication system with reduced risk of D2Dcongestion.

Further particular and preferred aspects of the present invention areset out in the accompanying independent and dependent claims. It will beappreciated that features of the dependent claims may be combined withfeatures of the independent claims in combinations other than thoseexplicitly set out in the claims.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, define, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

Respective features of the present disclosure are defined by thefollowing numbered paragraphs:

Paragraph 1. A method of operating a network entity in a wirelesstelecommunication system supporting device-to-device, D2D,communications between terminal devices, the method comprising:

-   -   establishing a set of radio resources to be made available for        D2D communications within the wireless telecommunication system;    -   communicating an indication of the set of radio resources to        terminal devices operating in the wireless telecommunications        system;    -   determining an indication of an extent to which the set of radio        resources is being used for D2D communications;    -   establishing an updated set of radio resources to be made        available for D2D communications within the wireless        telecommunication system based on the indication of the extent        to which the set of radio resources is being used for D2D        communications; and    -   communicating an indication of the updated set of radio        resources to terminal devices operating within the wireless        telecommunications system.

Paragraph 2. The method of paragraph 1, wherein the indication of theextent to which the set of radio resources is being used for D2Dcommunications is determined from feedback received from one or moreterminal devices regarding the extent to which the set of radioresources is being used for D2D communications.

Paragraph 3. The method of paragraph 2, wherein the feedback comprisesradio resource control, RRC, signalling.

Paragraph 4. The method of paragraph 2 or 3, wherein the feedbackreceived from a terminal device comprises an indication the terminaldevice has been restricted in an attempt to make use of radio resourceswithin the set of radio resources for D2D communication.

Paragraph 5. The method of paragraph 2, 3 or 4, wherein the feedbackreceived from a terminal device comprises an indication of measurementsmade by the terminal device of the extent to which the set of radioresources is being used for D2D communications.

Paragraph 6. The method of paragraph 5, wherein the feedback is receivedin response to the network entity transmitting a request for theterminal device to provide the feedback.

Paragraph 7. The method of paragraph 5 or 6, wherein the feedback isreceived in accordance with a predefined measurement schedule.

Paragraph 8. The method of paragraph 5, 6 or 7, wherein the feedback isreceived in response to the terminal device determining the extent towhich the set of radio resources is being used for D2D communicationsexceeds a predefined threshold.

Paragraph 9. The method of any of paragraphs 1 to 8, wherein theindication of the extent to which the set of radio resources is beingused for D2D communications is determined from the network entitymeasuring the extent to which the set of radio resources is being usedfor D2D communications.

Paragraph 10. The method of any of paragraphs 1 to 9, wherein the stepof establishing an updated set of radio resources comprises increasingthe amount of radio resources to be made for D2D communications if theindication of the extent to which the set of radio resources is beingused for D2D communications indicates more than an upper thresholdamount of the set of radio resources is being used and/or wherein thestep of establishing an updated set of radio resources comprisesdecreasing the amount of radio resources to be made available for D2Dcommunications if the indication of the extent to which the set of radioresources is being used for D2D communications indicates less than alower threshold amount of the set of radio resources is being used.

Paragraph 11. The method of any of paragraphs 1 to 10, furthercomprising:

-   -   determining an indication of an extent to which the updated set        of radio resources is being used for D2D communications;    -   establishing a further updated set of radio resources to be made        available for D2D communications within the wireless        telecommunication system based on the indication of the extent        to which the updated set of radio resources is being used for        D2D communications; and    -   communicating an indication of the further updated set of radio        resources to terminal devices operating within the wireless        telecommunications system.

Paragraph 12. The method of any of paragraphs 1 to 11, furthercomprising the network entity transmitting one or more radio resourceallocation messages to one or more terminal devices to indicate radioresources from within the set of radio resources to be used by the oneor more terminal devices for D2D transmissions.

Paragraph 13. The method of any of paragraphs 1 to 12, wherein thenetwork entity is a base station.

Paragraph 14. A network entity for use in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, wherein the network entity comprises a controller unit and atransceiver unit configured to operate together to:

-   -   establish a set of radio resources to be made available for D2D        communications within the wireless telecommunication system;    -   communicate an indication of the set of radio resources to        terminal devices operating in the wireless telecommunications        system;    -   determine an indication of an extent to which the set of radio        resources is being used for D2D communications;    -   establish an updated set of radio resources to be made available        for D2D communications within the wireless telecommunication        system based on the indication of the extent to which the set of        radio resources is being used for D2D communications; and    -   communicate an indication of the updated set of radio resources        to terminal devices operating within the wireless        telecommunications system.

Paragraph 15. Circuitry for a network entity for use in a wirelesstelecommunication system supporting device-to-device, D2D,communications between terminal devices, wherein the circuitry comprisesa controller element and a transceiver element configured to operatetogether to cause the network entity to:

-   -   establish a set of radio resources to be made available for D2D        communications within the wireless telecommunication system;    -   communicate an indication of the set of radio resources to        terminal devices operating in the wireless telecommunications        system;    -   determine an indication of an extent to which the set of radio        resources is being used for D2D communications;    -   establish an updated set of radio resources to be made available        for D2D communications within the wireless telecommunication        system based on the indication of the extent to which the set of        radio resources is being used for D2D communications; and    -   communicate an indication of the updated set of radio resources        to terminal devices operating within the wireless        telecommunications system.

Paragraph 16. A method of operating a terminal device in a wirelesstelecommunication system supporting device-to-device, D2D,communications between terminal devices, the method comprising:

-   -   receiving an indication of a set of radio resources available        for D2D communications within the wireless telecommunication        system from a network entity;    -   determining an indication of an extent to which the set of radio        resources is being used for D2D communications; and    -   transmitting the indication of the extent to which the set of        radio resources is being used for D2D communications to the        network entity.

Paragraph 17. The method of paragraph 16, wherein the indication of theextent to which the set of radio resources is being used for D2Dcommunications comprises radio resource control, RRC, signalling.

Paragraph 18. The method of paragraph 16 or 17, wherein the step ofdetermining an indication of an extent to which the set of radioresources is being used for D2D communications comprises the terminaldevice determining it has been restricted in an attempt to use radioresources within the set of radio resources for D2D communication.

Paragraph 19. The method of any of paragraphs 16 to 18, wherein theterminal device determining it has been restricted in an attempt to useradio resources comprises the terminal device determining it has beenprevented from using the set of radio resources to make a D2Dtransmission.

Paragraph 20. The method of any of paragraphs 16 to 19, wherein theterminal device determining it has been restricted in an attempt to useradio resources comprises the terminal device determining it wasrequired to wait for more than a predefined delay before being able touse the set of radio resources to make a D2D transmission.

Paragraph 21. The method of any of paragraphs 16 to 20, wherein theterminal device determining it has been restricted in an attempt to useradio resources comprises the terminal device determining there was lessthan a predefined amount of the set of radio resources remainingavailable for use by the terminal device to make a D2D transmission.

Paragraph 22. The method of any of paragraphs 16 to 21, furthercomprising the terminal device measuring the extent to which the set ofradio resources is being used for D2D communications and determining theindication of the extent to which the set of radio resources is beingused for D2D communications therefrom.

Paragraph 23. The method of paragraph 22, wherein the terminal devicemeasures the extent to which the set of radio resources is being usedfor D2D communications in response to receiving from the network entitya request to transmit the indication of the extent to which the set ofradio resources is being used for D2D communications.

Paragraph 24. The method of paragraph 22 or 23, wherein the terminaldevice measures the extent to which the set of radio resources is beingused for D2D communications in accordance with a predefined measurementschedule.

Paragraph 25. The method of paragraph 22, 23 or 24, wherein the terminaldevice transmits the indication of the extent to which the set of radioresources is being used for D2D communications to the network entity inresponse to the terminal device determining from the measurements theextent to which the set of radio resources is being used for D2Dcommunications exceeds a predefined threshold.

Paragraph 26. The method of any of paragraphs 16 to 25, furthercomprising receiving an indication of an updated set of radio resourcesavailable for D2D communications within the wireless telecommunicationsystem from the network entity;

-   -   determining an indication of an extent to which the updated set        of radio resources is being used for D2D communications; and    -   transmitting the indication of the extent to which the updated        set of radio resources is being used for D2D communications to        the network entity.

Paragraph 27. The method of any of paragraphs 16 to 26, furthercomprising receiving from the network entity one or more radio resourceallocation messages to indicate radio resources selected from within theset of radio resources to be used by the terminal device for one or moreD2D transmissions.

Paragraph 28. The method of any of paragraphs 16 to 27, furthercomprising the terminal device selecting radio resources from within theset of radio resources to use for one or more D2D transmissions.

Paragraph 29. The method of paragraph 28, further comprising making theone or more D2D transmissions using the radio resources selected fromwithin the set of radio resources.

Paragraph 30. A terminal device for use in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, wherein the terminal device comprises a controller unit and atransceiver unit configured to operate together to:

-   -   receive an indication of a set of radio resources available for        D2D communications within the wireless telecommunication system        from a network entity;    -   determine an indication of an extent to which the set of radio        resources is being used for D2D communications; and    -   transmit the indication of the extent to which the set of radio        resources is being used for D2D communications to the network        entity.

Paragraph 31. Circuitry for a terminal device for use in a wirelesstelecommunication system supporting device-to-device, D2D,communications between terminal devices, wherein the circuitry comprisesa controller element and a transceiver element configured to operatetogether to cause the terminal device to:

-   -   receive an indication of a set of radio resources available for        D2D communications within the wireless telecommunication system        from a network entity;    -   determine an indication of an extent to which the set of radio        resources is being used for D2D communications; and    -   transmit the indication of the extent to which the set of radio        resources is being used for D2D communications to the network        entity.

Paragraph 32. A method of operating a terminal device in a wirelesstelecommunication system supporting device-to-device, D2D,communications between terminal devices, the method comprising:

-   -   receiving an indication of a set of radio resources available        for D2D communications within the wireless telecommunication        system from a network entity;    -   monitoring the set of radio resources to determine if another        terminal device is seeking to communicate with the terminal        device in a D2D manner using the set of radio resources;    -   receiving an indication of an updated set of radio resources        available for D2D communications within the wireless        telecommunication system from the network entity; and    -   monitoring the updated set of radio resources to determine if        another terminal device is seeking to communicate with the        terminal device in a D2D manner using the set of radio        resources.

Paragraph 33. A terminal device for use in a wireless telecommunicationsystem supporting device-to-device, D2D, communications between terminaldevices, wherein the terminal device comprises a controller unit and atransceiver unit configured to operate together to:

-   -   receive an indication of a set of radio resources available for        D2D communications within the wireless telecommunication system        from a network entity;    -   monitor the set of radio resources to determine if another        terminal device is seeking to communicate with the terminal        device in a D2D manner using the set of radio resources;    -   receive an indication of an updated set of radio resources        available for D2D communications within the wireless        telecommunication system from the network entity; and    -   monitor the updated set of radio resources to determine if        another terminal device is seeking to communicate with the        terminal device in a D2D manner using the set of radio        resources.

Paragraph 34. Circuitry for a terminal device for use in a wirelesstelecommunication system supporting device-to-device, D2D,communications between terminal devices, wherein the circuitry comprisesa controller element and a transceiver element configured to operatetogether to cause the terminal device to:

-   -   receive an indication of a set of radio resources available for        D2D communications within the wireless telecommunication system        from a network entity;    -   monitor the set of radio resources to determine if another        terminal device is seeking to communicate with the terminal        device in a D2D manner using the set of radio resources;    -   receive an indication of an updated set of radio resources        available for D2D communications within the wireless        telecommunication system from the network entity; and    -   monitor the updated set of radio resources to determine if        another terminal device is seeking to communicate with the        terminal device in a D2D manner using the set of radio        resources.

REFERENCES

-   [1] LTE for UMTS: OFDMA and SC-FDMA Based Radio Access, Harris Holma    and Antti Toskala, Wiley 2009, ISBN 978-0-470-99401-6.-   [2] R2-133840, “CSMA/CA based resource selection,” Samsung,    published at 3GPP TSG-RAN WG2 #84, San Francisco, USA, 11-15 Nov.    2013.-   [3] R2-133990, “Network control for Public Safety D2D    Communications”, Orange, Huawei, HiSilicon, Telecom Italia,    published at 3GPP TSG-RAN WG2 #84, San Francisco, USA, 11-15    November 2013.-   [4] R2-134246, “The Synchronizing Central Node for Out of Coverage    D2D Communication”, General Dynamics Broadband UK, published at 3GPP    TSG-RAN WG2 #84, San Francisco, USA, 11-15 Nov. 2013.-   [5] R2-134426, “Medium Access for D2D communication”, LG Electronics    Inc, published at 3GPP TSG-RAN WG2 #84, San Francisco, USA, 11-15    Nov. 2013.-   [6] R2-134238,”.-   [8] R2-134431, “Simulation results for D2D voice services using    connectionless approach”, General Dynamics Broadband UK, published    at 3GPP TSG-RAN WG2 #84, San Francisco, USA, 11-15 Nov. 2013.-   [9] “D2D Resource Allocation under the Control of BS”, Xiaogang R.    et al, University of Electronic Science and Technology of China,    https//mentor.ieee.org/802.16/dcn/13/16-13-0123-02-000n-d2d-resource-allocation-under-the-control-of-bs.docx-   [10] US 2013/0170387-   [11] US 2012/0300662

1. Circuitry for a terminal device for use in a wirelesstelecommunication system supporting device-to-device (D2D)communications between terminal devices, wherein the circuitry isconfigured to: receive an indication of a set of radio resourcesavailable for D2D communications within the wireless telecommunicationsystem from a network entity; determine an indication of an extent towhich the set of radio resources is being used for D2D communications;and transmit the indication of the extent to which the set of radioresources is being used for D2D communications to the network entity. 2.The circuitry of claim 1, wherein the indication of the extent to whichthe set of radio resources is being used for D2D communicationscomprises radio resource control (RRC) signalling.
 3. The circuitry ofclaim 1, wherein the circuitry is configured to: determine an indicationof an extent to which the set of radio resources is being used for D2Dcommunications by determining that the terminal device has beenrestricted in an attempt to use radio resources within the set of radioresources for D2D communication.
 4. The circuitry of claim 3, whereinthe circuitry is configured to: determine that the terminal device hasbeen restricted in an attempt to use radio resources by determining thatthe terminal device has been prevented from using the set of radioresources to make a D2D transmission.
 5. The circuitry of claim 3,wherein the circuitry is configured to: determine that the terminaldevice has been restricted in an attempt to use radio resources bydetermining that the terminal device was required to wait for more thana predefined delay before being able to use the set of radio resourcesto make a D2D transmission.
 6. The circuitry of claim 3, wherein thecircuitry is configured to: determine that the terminal device has beenrestricted in an attempt to use radio resources by determining there wasless than a predefined amount of the set of radio resources remainingavailable for use by the terminal device to make a D2D transmission. 7.The circuitry of claim 1, wherein the circuitry is configured to:measure the extent to which the set of radio resources is being used forD2D communications; and determine the indication of the extent to whichthe set of radio resources is being used for D2D communications based onthe measured extent to which the set of radio resources is being usedfor D2D communications.
 8. The circuitry of claim 7, wherein thecircuitry is configured to: measure the extent to which the set of radioresources is being used for D2D communications in response to receiving,from the network entity, a request to transmit the indication of theextent to which the set of radio resources is being used for D2Dcommunications.
 9. The circuitry of claim 7, wherein the circuitry isconfigured to: measure the extent to which the set of radio resources isbeing used for D2D communications in accordance with a predefinedmeasurement schedule.
 10. The circuitry of claim 7, wherein thecircuitry is configured to: transmit the indication of the extent towhich the set of radio resources is being used for D2D communications tothe network entity in response to the circuitry determining, from themeasurements, the extent to which the set of radio resources is beingused for D2D communications exceeds a predefined threshold.
 11. Thecircuitry of claim 1, wherein the circuitry is configured to: receive anindication of an updated set of radio resources available for D2Dcommunications within the wireless telecommunication system from thenetwork entity; determine an indication of an extent to which theupdated set of radio resources is being used for D2D communications; andtransmit the indication of the extent to which the updated set of radioresources is being used for D2D communications to the network entity.12. The circuitry of claim 1, wherein the circuitry is configured to:receive from the network entity one or more radio resource allocationmessages to indicate radio resources selected from within the set ofradio resources to be used by the terminal device for one or more D2Dtransmissions.
 13. The circuitry of claim 1, wherein the circuitry isconfigured to: select radio resources from within the set of radioresources to use for one or more D2D transmissions.
 14. The method ofclaim 13, wherein the circuitry is configured to: make the one or moreD2D transmissions using the radio resources selected from within the setof radio resources.
 15. A terminal device for use in a wirelesstelecommunication system supporting device-to-device (D2D)communications between terminal devices, wherein the terminal devicecomprises: circuitry configured to receive an indication of a set ofradio resources available for D2D communications within the wirelesstelecommunication system from a network entity; monitor the set of radioresources to determine if another terminal device is seeking tocommunicate with the terminal device in a D2D manner using the set ofradio resources; receive an indication of an updated set of radioresources available for D2D communications within the wirelesstelecommunication system from the network entity; and monitor theupdated set of radio resources to determine if another terminal deviceis seeking to communicate with the terminal device in a D2D manner usingthe set of radio resources.
 16. Circuitry for a terminal device for usein a wireless telecommunication system supporting device-to-device (D2D)communications between terminal devices, wherein the circuitry isconfigured to: receive an indication of a set of radio resourcesavailable for D2D communications within the wireless telecommunicationsystem from a network entity; monitor the set of radio resources todetermine if another terminal device is seeking to communicate with theterminal device in a D2D manner using the set of radio resources;receive an indication of an updated set of radio resources available forD2D communications within the wireless telecommunication system from thenetwork entity; and monitor the updated set of radio resources todetermine if another terminal device is seeking to communicate with theterminal device in a D2D manner using the set of radio resources.